1. Field of the Invention
This invention relates to a clutch mechanism and, more particularly to a friction clutch mechanism wherein a driving member is coupled to a driven member using clutch pins and the clutch is switched on and off utilizing a frictional force of a friction plate.
2. Description of the Related Art
A clutch mechanism is a mechanical device for selectively connecting a driving member and a driven member, and various types, such as a friction clutch type, are used. Among these, there are those wherein when the driving member is rotated, the driving and driven members are coupled so that power can be transmitted from the driving member to the driven member, and when the driving member is stopped, the driving and driven members are uncoupled so that the driven member can rotate in both directions. This kind of clutch mechanism includes for example the xe2x80x9cFree Wheel Clutch and Apparatus Using Samexe2x80x9d disclosed in U.S. Pat. No. 4,909,365. The main features of this clutch mechanism are illustrated in FIG. 23 hereof.
The related art clutch mechanism 300 shown in FIG. 23 has an output shaft 302, which is a driving member, rotatably supported by a housing 301. The output shaft 302 projects outward from the housing 301. A friction plate 303 and a pinion 304, which is a driven member, are rotatably supported on the projecting part of the output shaft 302. In this clutch mechanism 300, a side face 305 of the friction plate 303 is pressed against a wall face 306 of the housing 301 with a predetermined force (thrust) F2, and the output shaft 302 and the pinion 304 are selectively coupled by the behavior of a clutch key 307 with respect to the output shaft 302 and the friction plate 303 and the pinion 304.
More specifically, in the clutch mechanism 300, a snap ring 308 is fitted to the end of the output shaft 302 projecting from the housing 301, a compression spring 309 is interposed between the snap ring 308 and the pinion 304, and by way of the pinion 304 the spring force of the compression spring 309 presses the side face 305 of the friction plate 303 against the wall face 306 of the housing 301. Also, a leg part 311 of the clutch key 307 is so fitted in the friction plate 303 that it can swing through a predetermined angle.
When the output shaft 302 rotate s, utilizing a frictional force arising between the housing 301 and the friction plate 303, the rotational timing of the friction plate 303 with respect to the output shaft 302 is delayed. As a result, the clutch key 307 swings in the front-rear direction of the drawing and couples the output shaft 302 with the pinion 304, enabling power to be transmitted between the two.
When the rotation of the output shaft 302 stops, the clutch key 307 uncouples the output shaft 302 from the pinion 304 and thereby renders the pinion n 304 rotatable in both directions.
However, this clutch mechanism of related art has had the following four problems:
Firstly, because the clutch mechanism 300 utilizes a frictional force between the housing 301 and the friction plate 303, to maintain a stable frictional force over a long period, it is necessary to consider wear of the contacting parts. In particular, when the output shaft 302 is to rotate at high speed, countermeasures to wear are even more important. And furthermore, because the contacting part of the friction plate 303 is exposed, the effect of dust and the like on its resistance to wear must be considered.
Secondly, because the clutch mechanism utilizes a frictional force obtained by pressing flat faces together, and the friction plate 303 having one of the flat faces rotates, to secure the frictional force it is necessary for the flatness and the assembly accuracy of the housing 301 and the friction plate 303 to be kept very high, and the dimensional management required is not easy.
Thirdly, because the clutch key 307, which has a complex shape, is swingably fitted in respective key grooves of the output shaft 302, the friction plate 303 and the pinion 304 to effect the clutch-ON operation, the structure of the clutch mechanism 300 is complex. Furthermore, the dimensional management of the key grooves and the clutch key 307 is not easy. Consequently, it is necessary for ample care to be taken always to engage the clutch mechanism 300 smoothly.
Fourthly, because the frictional force is produced by means of the spring force of a compression spring 309 fitted on the output shaft 302, the clutch mechanism 300 is large in the length direction of the output shaft 302.
It is therefore a first object of the present invention to provide a clutch mechanism wherein the frictional force between the housing side and the friction plate is stable.
It is a second o object of the invention to provide a clutch mechanism which is small and simple in construction, the dimensional management of which is easy, and which can always be engaged smoothly.
To achieve these and other objects, a first aspect of the invention provides a clutch mechanism comprising: a housing; a driving member, rotatably support ed by the housing a and having a plurality of cam grooves formed in an outer circumferential face thereof and extending in an axial direction thereof; a driven member, which can rotate coupled to the driving member and rotate freely uncoupled from the driving member; a disc-shaped friction plate, rotatably supported by the driving member and having in an inner circumferential face thereof a plurality of pin-holding grooves, facing the cam grooves and having their depths in a radial direction of the friction plate; tapered space parts, each formed by frictional engagement faces consisting of a bottom face of a respective cam groove and an inner circumferential face of the driven member; a plurality of clutch pins, each disposed partly in a tapered space part and partly between the cam groove forming that tapered space part and the pin-holding groove facing that cam groove; and an oil seal, interposed between an inner circumferential surface of the housing and an outer circumferential surface of the friction plate, for providing an action force tending to prevent the friction plate and, by extension, the clutch pins from moving; and a lubricant, filling a space enclosed by the housing, the friction plate and the oil seal, wherein when the driving member rotates, utilizing a frictional force on the friction plate, the clutch pins are engaged with the frictional engagement faces of the tapered space parts by a wedge action and the driving member and the driven member are thereby coupled so that power can be transmitted between them, and when the driving member stops, the driving member and the driven member cease to be coupled by the clutch pins and the driven member assumes an idling state with respect to the driving member.
Thus, in this invention, a friction plate is disposed in a housing, an oil seal is interposed between an inner circumferential surface of the housing and the outer circumferential surface of the friction plate, and the oil seal provides and action force tending to prevent the clutch pins from moving. That is, to produce a frictional force between the housing side and the friction plate, instead of a thrust force being made to act on the friction plate as in the related art, a radial force is applied. And because the frictional force is produced by an oil seal being fitted in contact with the outer circumferential surface of the friction plate and made to apply a contact force to the friction plate, the radius at which the frictional force acts can be made large. Accordingly, since a smaller frictional force is sufficient to provide the same frictional torque as in the related art described above, the contact pressure can be lowered and wear can be suppressed. As a result, the frictional force can be kept stable at all times. Furthermore, since the force providing the frictional torque acts in the radial direction, the length direction dimension of the driving member can be made small and the clutch mechanism can be made compact. Also, because a lip of the oil seal makes contact with the outer circumferential surface of the friction plate, there is no need for a high assembly accuracy and the dimensional management of the components becomes easy.
Also, a space enclosed by the housing, the friction plate and the oil seal is filled with a lubricant, and wear of the contacting parts is further suppressed by the part of the outer circumferential surface of the friction plate with which the lip of the oil seal makes contact being lubricated by the lubricant. As a result, the frictional force between the mating parts is stable. And therefore, even if the driving member rotates at a high speed during use, the clutch mechanism operates reliably. Because of this, the clutch mechanism can be used in a stable state over a wide speed range from low speeds to high speeds. Also, because the friction plate is disposed in the housing, where the installation environment is good, wear of the clutch mechanism caused by dust and the like from outside is prevented and the durability of the clutch mechanism can be increased.
Also, the pin-holding grooves are formed in the friction plate, whose rotation timing is delayed with respect to the driving member, and the clutch pins are held with these pinholding grooves. Consequently, even when with the friction plate stopped the driving member starts to rotate, the clutch pins do not immediately rotate with the driving member. As a result, the clutch pins are locked by a wedge action between the frictional engagement faces of the tapered space parts, the driving and driven members are coupled and the clutch is thereby switched ON. Because it works just by clutch pins of a simple shape being coupled with or uncoupled from the cam grooves in the driving member, the inner circumferential surface of the driven member and the pin-holding grooves of the friction plate, the clutch mechanism has a simple construction and can always be engaged smoothly. Furthermore, because the simple clutch pins are not sprung as in the related art described above but simply couple, uncouple or hold by way of the cam grooves and the pin-holding grooves, the groove shapes are also simple, dimensional management is easy, and manufacturability is good. And grooves for coupling with the clutch pins are not needed in the driven member.
If the bottom face of each of the cam grooves is made to have an arcuate face swelling toward the opening of the cam groove, the slope of the bottom face can be made gentle in the vicinity of the peak of the arcuate face and steeper with progress away from the peak. When this is done, the range of the half-clutch state is narrow, and the clutch mechanism can be switched rapidly without strain. And because the whole of the bottom face is a gentle arcuate face, the operation of switching between clutch-ON and clutch-OFF becomes smooth.
A second aspect of the invention provides a clutch mechanism comprising: a housing; a driven member, rotatably supported by the housing; a driving member, which can rotate coupled to the driven member and rotate freely, uncoupled f from the driving member, having a plurality of cam grooves formed in an inner circumferential face thereof and extending in an axial direction thereof; a disc-shaped friction plate, rotatably supported by the driven member and having in an inner circumferential face thereof a plurality of pin-holding grooves, facing the cam grooves and having their depths in a radial direction; tapered space parts, each formed by frictional engagement faces consisting of a bottom face of a cam groove and an outer circumferential face of the driven member; a plurality of clutch pins, each disposed partly in a tapered space part and partly between the cam groove forming that tapered space part and the pin-holding groove facing that cam groove; an oil seal, interposed between an inner circumferential surface of the housing and an outer circumferential surface of the friction plate, for providing an action force tending to prevent the clutch pins from moving; and a lubricant, filling a space enclosed by the housing, the friction plate and the oil seal, wherein when the driving member rotates, utilizing a frictional force on the friction plate, the clutch pins are engaged with the frictional engagement faces of the tapered space parts by a wedge action and the driving member and the driven member are coupled so that power can be transmitted from the driving member to the driven member, and when the driving member stops, the driving member and the driven member cease to be coupled by the clutch pins and the driven member assumes an idling state with respect to the driving member.